Chapter 4 Anatomy and Physiology of the Muscles
Muscle Physiology
The Structure and Organization
of Skeletal Muscle
T
he structure of muscle fibers (or muscle cells) and the con-
nection between the muscle and the nerves can be ana-
lyzed by looking at the muscle as a whole and then break-
ing it down into its’ smaller components or layers. Each layer of
muscle tissue is surrounded by a wrapping of connective tissue,
or fascia, much like a wrapping of cellophane. These many lay-
ers of fascia come together at the ends of the muscle and extend
beyond to form the tendon sheaths, or tendons (A on previous
page), which attach the muscle to the periosteum of the bone.The main bulk of the muscle is called the muscle belly (C) and it is
wrapped in connective tissue called the epimysium (B). Within the
muscle belly are smaller bundles of muscle fibers, called fasciculi
(D), and these are wrapped in the perimysium. The individual
muscle fibers or muscle cells (E) are no larger than strands of hair
and are surrounded by the endomysium and sarcolemma. The
muscle fiber is a cylindrical cell and it varies in length from a few
millimetres in the eye, up to approximately 30 centimetres in the
sartorius muscle^1.Each muscle fiber is made up of smaller myofibrils (F), which ex-
tend the entire length of the fiber. The myofibrils contain the con-
tractile components of the muscle, the myosin (G) and actin (H)
protein filaments or myofilaments. Actin is thin and light in color
while myosin is thick and dark. They interlink repeatedly along
the myofibril, giving the muscle a striated look. Each actin filament
contains a Z-disc, (dense connective tissue regions shaped like
pancakes) which divide the myofibril into compartments known as
sarcomeres (the area between two Z-discs).It is within the sarcomeres that the contraction or shortening
occurs, so the sarcomere is known as the functional and main
contractile unit of the muscle fiber.